Chapter5-RevSJ_-_Tagged

Chapter 5: Lipids

Learning Outcomes

• Define lipids: Classify lipids by structure, including types such as triglycerides, phospholipids, and sterols

• Digestion and absorption: Explain digestion, absorption, and transport of lipids in the body, with specific focus on process and enzymes involved

• Functions of lipids: Outline the various roles lipids play in bodily functions, including energy storage, organ insulation, and more

• Dietary recommendations: Identify recommended intake for total fat, saturated fat, trans fat, essential fatty acids, and cholesterol

• Food sources: Differentiate between good, bad, and alternative sources of dietary fats, like sources of omega-3 versus omega-6 fatty acids

• Health implications: Describe the development of atherosclerosis and coronary heart disease, emphasizing lifestyle factors affecting risk

Introduction to Lipids

• Quiz Highlights:

  • Both excessive and insufficient fat can harm health, which can lead to obesity or deficiency diseases.

  • Fatty acids typically have even carbon numbers; common examples include palmitic acid (C16) and stearic acid (C18).

  • Triglycerides consist of glycerol and three fatty acid tails, and they are the main form of fat storage in the body.

  • Fats provide 9 kcalories per gram, while carbohydrates and proteins provide 4 kcalories per gram.

What Are Lipids?

Classification:

• Types include:

  • Triglycerides: The most common form of fat in the diet and body, made from glycerol and three fatty acids.

  • Phospholipids: Important for cell membrane structure, made of glycerol, two fatty acids, and a phosphate group.

  • Sterols: Complex compounds like cholesterol, which is vital for hormone production and cellular function.

• Chemical Composition:

  • Composed of carbon, hydrogen, and oxygen in various ratios.

• Hydrophobic Nature:

  • Lipids do not dissolve in water, which is crucial for their role in cellular membranes.

Basic Functions of Lipids:

• Energy Storage and Provision: Store energy for long-term use (e.g., adipose tissue).

• Insulation: Maintain body temperature and protect internal organs (e.g., subcutaneous fat).

• Steroid and Bile Production: Cholesterol is a precursor to steroid hormones (e.g., testosterone, estrogen).

• Transportation of Fat-Soluble Nutrients: Lipids assist in the absorption of vitamins A, D, E, and K.

• Structural Role in Cell Membranes: Phospholipids form the lipid bilayer of cells, allowing selective permeability.

Fatty Acids

• Building Blocks: Essential components of triglycerides and phospholipids.

• Structure:

  • Consists of a carbon chain with a carboxyl group (alpha end) and a methyl group (omega end).

• Caloric Density: Fatty acids have a higher caloric density (9 kcal/g) compared to carbohydrates or proteins (4 kcal/g).

• Variability:

  • Fatty acids vary based on their chain length, saturation level, and shape (cis vs. trans configuration).

Types of Fatty Acids

Chain Length Variations:

• Short-chain: 2-4 carbons, found in dairy fats.

• Medium-chain: 6-10 carbons; coconut oil is a notable example.

• Long-chain: 12 or more carbons (most common in foods); examples include oleic acid (C18) from olive oil.

Degree of Saturation:

• Saturated: No double bonds; examples include butter and lard, which are solid at room temperature.

• Unsaturated: One (monounsaturated, e.g., olive oil) or multiple (polyunsaturated, e.g., fish oil) double bonds; liquid at room temperature.

Stability of Fatty Acids

• Rancidity: Spoiling of fats through oxidation; unsaturated fats spoil faster than saturated fats.

• Enhancing Stability: Techniques include the use of antioxidants (e.g., Vitamin E), minimizing exposure to oxygen, heat, and light, and hydrogenation (converting liquid oils into solid fats).

Double Bond Locations

Omega-3 vs Omega-6:

• Omega-3: First double bond between the third and fourth carbons; important sources include fatty fish (salmon, mackerel) and flaxseeds (alpha-linolenic acid).

• Omega-6: First double bond between the sixth and seventh carbons; commonly found in vegetable oils (e.g., sunflower oil, linoleic acid).

Triglycerides

• Structure: Comprised of three fatty acids attached to a glycerol backbone.

• Functions Include:

  • Adding texture to foods (e.g., creaminess in ice cream).

  • Tenderizing meats through fat marbling.

  • Storing energy in adipose tissue, which serves as a reserve fuel source for the body.

Phospholipids and Sterols

Phospholipids:

• Comprised of glycerol, two fatty acids, and a phosphate group; critical for forming cell membranes and ensuring cell integrity.

Sterols:

• Complex compounds with four carbon rings; cholesterol is a notable example, necessary for hormone production (e.g., cortisol and sex hormones) and maintaining cell membrane fluidity.

Digestion and Absorption of Lipids

• Starting with Triglycerides: These are the major form of dietary lipids; they are digested into fatty acids, glycerol, and monoglycerides.

• Lipase Enzymes: Critical for lipid digestion; the process begins in the mouth (lingual lipase), continues in the stomach (gastric lipase), and predominantly in the small intestine where bile emulsifies fats for better digestion.

Transportation of Lipids

• Lipid Absorption: Varied based on fatty acid structure; short- and medium-chain fatty acids enter the bloodstream directly, whereas long-chain fatty acids reform into chylomicrons before entering the lymphatic system.

• Lipoproteins: Four types (Chylomicrons, VLDLs, LDLs, HDLs) transport lipids in the blood, influencing cardiovascular health through their composition and density (e.g., HDL is considered "good" cholesterol).

Functions of Lipids in the Body

• Provide energy, form structures of cell membranes, regulate metabolism, enhance absorption of fat-soluble vitamins, insulate the body, and cushion internal organs (e.g., brain is surrounded by fat for protection).

Dietary Fat Recommendations

• General Intake: Between 20-35% of daily caloric intake should be from fat.

• Limit Saturated Fat: To <10% of total kilocalories, trans fats to <1%; avoid products with partially hydrogenated oils.

• Essential Fatty Acids: Include Linoleic (5-10%) and ALA (0.6-1.2%) for optimal health.

Heart Disease and Risk Factors

• Atherosclerosis: Begins with arterial injury, leading to cholesterol accumulation and plaque formation, which narrows arteries.

• Influential Factors: Age, gender, family history, blood pressure, and dietary habits, such as high saturated fat intake.

Strategies to Lower Heart Disease Risk

• Lifestyle Changes: Regular exercise, healthy eating (rich in fruits, vegetables, whole grains), and avoiding smoking have protective effects on heart health.

Conclusion

• Understanding the roles and functions of lipids fosters better dietary choices, promoting cardiovascular health and overall well-being. By recognizing both good and bad fat sources, individuals can make informed choices to enhance their health.